The present invention relates to processes of preparing conditioned organic pigments with one or more acrylic polymer dispersants.
Crude organic pigments are obtained after chemical synthesis and are generally unsuitable for use as pigments in coating formulations. Consequently, crude organic pigments undergo one or more finishing steps that modify particle size, particle shape, surface characteristics, and/or crystal structure of the pigment in such a way that provides a pigment of good pigmentary quality. See, for example, W. Carr, xe2x80x9cImproving the Physical Properties of Pigmentsxe2x80x9d in Pigment Handbook, Vol. III (New York: John Wiley and Sons, Inc., 1973), pages 29-35; W. Herbst and K. Hunger, Industrial Organic Pigments (New York: VCH Publishers, Inc., 1993), pages 205-207; R. B. McKay, xe2x80x9cThe Development of Organic Pigments with Particular Reference to Physical Form and Consequent Behavior in Usexe2x80x9d in Rev. Prog. Coloration, 10, 25-32 (1979); and R. B. McKay, xe2x80x9cControl of the application performance of classical organic pigmentsxe2x80x9d in JOCCA, 89-93 (1989) herein incorporated by reference. In some finishing processes, one or more of the finishing steps can include a strong mineral acid or caustic alkali, followed by precipitation of the pigment, and/or milling the crude pigment. A pigment conditioning process that avoids a strong acid or caustic step would be desirable because elimination of such a step would significantly reduce environmental and health risks associated with caustic chemicals and lower costs associated with pigment conditioning processes. Crude organic pigments having undergone a pigment conditioning process are called conditioned organic pigments and are typically sold commercially.
Milling methods are known to improve various properties of organic pigments. E.g., U.S. Pat. Nos. 5,614,014, 5,626,662, and 5,704,556. However, milling in the presence of acrylic polymers as specified in the present invention has not previously been described.
Acrylic copolymers have been used to disperse and maintain, in a dispersed state, conditioned organic pigments in coatings and other materials. See U.S. Pat. Nos. 5,859,113 and 5,219,945, as well as U.S. Pat. Nos. 4,293,475, 4,597,794, 4,734,137, 5,530,043, and 5,629,367, herein incorporated by reference. These dispersions are combined with other components (such as resins and other additives) to form paints and other coatings and other materials. Although dispersing agents have been used to disperse conditioned organic pigments in liquid dispersions, very little is known about the use of copolymer dispersants during processes of conditioning crude organic pigments prior to their isolation as dry powders. U.S. Pat. No. 3,806,464 discloses a method for encapsulating pigments with acrylic polymers and U.S. Pat. No. 4,734,137 discloses a method for reprecipitating pigments that have been dissolved in solvents containing caustic alkali and acrylic resins. Neither patent, however, discloses a milling process, a critical feature of the present invention that provides readily dispersible pigments under relatively gentle conditions.
The present invention relates to a process for making conditioned organic pigments using at least one acrylic copolymer dispersant. In certain embodiments, these processes may avoid the need for the normal processes requiring the use of strong acids having a pH of less than 2. The conditioned organic pigments formed from the processes of the present invention may be used, in part, in pigmented formulations such as coating compositions, paints and printing inks. The process comprises
(a) milling a mixture comprising:
(1) one or more crude organic pigments;
(2) at least about 0.1 % by weight, relative to the organic pigment, of one or more acrylic copolymer dispersants (preferably containing at least one polymerized monomer having an aromatic functionality in an adsorbing segment); and
(3) 0 to about 100 parts by weight, relative to the organic pigment, of a milling liquid in which the organic pigment is substantially insoluble; and
(b) isolating the milled organic pigment.
The milling mixture may also include one or more of the following:
(4) one or more milling additives; and/or
(5) one or more surface treatment additives.
Upon completion of the milling, one or more of the following may be added to flocculate the milled pigment prior to isolation:
(6) one or more acids;
(7) one or more divalent metal salts; and/or
(8) one or more quaternary ammonium salts.
All pigments produced from the processes of the present invention are highly dispersible and provide enhanced color in wet and/or dried coating systems.
The term xe2x80x9ccrude organic pigmentxe2x80x9d as used herein refers to an organic pigment that has not been treated using the process of the present invention. Such crude organic pigments may or may not be modified after chemical synthesis and may or may not have desirable coloristic properties in coatings systems.
The term xe2x80x9cconditioned organic pigmentxe2x80x9d as used herein refers to an organic pigment that is modified by the process of the present invention after chemical synthesis.
Processes of the present invention require milling a crude organic pigment or reprocessing of a finished organic pigment with one or more acrylic polymer dispersants, an optional milling liquid, and optionally one or more milling additives, followed by isolation. The components of the milling mixture may be added or combined in any order such that preferably (but not necessarily) all are present at the start of the milling. Suitable milling methods include dry-milling methods, such as jet milling, ball milling, and the like, and wet-milling methods, such as salt kneading, sand milling, bead milling, and the like in a milling liquid. The resultant organic pigments contain readily dispersible individual particles or loosely bound aggregates.
Crude Organic Pigments
Crude organic pigments used in the practice of the present invention include perylenes, quinacridones, phthalocyanines, isoindolines, dioxazines (that is, triphenedioxazines), 1,4-diketopyrrolopyrroles, anthrapyrimidines, anthanthrones, flavanthrones, indanthrones, perinones, pyranthrones, thioindigos, 4,4xe2x80x2-diamino-1,1xe2x80x2-dianthraquinonyl, and azo compounds, as well as substituted derivatives thereof. Preferred organic pigments are aromatic pigments such as perylene, quinacridone, phthalocyanine, isoindoline, and dioxazine pigments. Mixtures, including solid solutions, may also be prepared.
Perylene pigments used in the practice of the present invention may be unsubstituted or substituted. Substituted perylenes may be substituted at imide nitrogen atoms for example, and substituents may include an alkyl group of 1 to 10 carbon atoms, an alkoxy group of 1 to 10 carbon atoms and a halogen (such as chlorine) or combinations thereof. Substituted perylenes may contain more than one of any one substituent. The diimides and dianhydrides of perylene-3,4,9,10-tetracarboxylic acid are preferred. Crude perylenes can be prepared by methods known in the art. Please review, W. Herbst and K. Hunger, Industrial Organic Pigments (New York: VCH Publishers, Inc., 1993), pages 9 and 467-475, H. Zollinger, Color Chemistry (VCH Verlagsgessellschaft, 1991), pages 227-228 and 297-298, and M. A. Perkins, xe2x80x9cPyridines and Pyridonesxe2x80x9d in The Chemistry of Synthetic Dyes and Pigments, ed. H. A. Lubs (Malabar, Fla.: Robert E. Krieger Publishing Company, 1955), pages 481-482, incorporated herein by reference.
Phthalocyanine pigments, especially metal phthalocyanines may be used in the practice of the present invention. Although copper phthalocyanines are preferred, other metal-containing phthalocyanine pigments, such as those based on zinc, cobalt, iron, nickel, and other such metals, may also be used. Metal-free phthalocyanines are also suitable but are generally less preferred. Phthalocyanine pigments may be unsubstituted or partially substituted, for example, with one or more alkyl (having 1 to 10 carbon atoms), alkoxy (having 1 to 10 carbon atoms), halogens such as chlorine, or other substituents typical of phthalocyanine pigments. Crude phthalocyanines may be prepared by any of several methods known in the art. They are preferably prepared by a reaction of phthalic anhydride, phthalonitrile, or derivatives thereof, with a metal donor, a nitrogen donor (such as urea or the phthalonitrile itself), and an optional catalyst, preferably in an organic solvent. E.g., W. Herbst and K. Hunger, Industrial Organic Pigments (New York: VCH Publishers, Inc., 1993), pages 418-427, H. Zollinger, Color Chemistry (VCH Verlagsgessellschaft, 1991), pages 101-104, and N. M. Bigelow and M. A. Perkins, xe2x80x9cPhthalocyanine Pigmentsxe2x80x9d in The Chemistry of Synthetic Dyes and Pigments, ed. H. A. Lubs (Malabar, Fla.: Robert E. Krieger Publishing Company, 1955), pages 584-587; see also U.S. Pat. Nos. 4,158,572, 4,257,951, and 5,175,282 and British Patent 1,502,884, incorporated herein by reference.
Quinacridone pigments, as used herein, include unsubstituted or substituted quinacridones (for example, with one or more alkyl, alkoxy, halogens such as chlorine, or other substituents typical of quinacridone pigments), and are suitable for the practice of the present invention. The quinacridone pigments may be prepared by any of several methods known in the art but are preferably prepared by thermally ring-closing various 2,5-dianilinoterephthalic acid precursors in the presence of polyphosphoric acid. E.g., S. S. Labana and L. L. Labana, xe2x80x9cQuinacridonesxe2x80x9d in Chemical Review, 67, 1-18 (1967), and U.S. Pat. Nos. 3,157,659, 3,256,285, 3,257,405, and 3,317,539.
Isoindoline pigments, which can optionally be substituted symmetrically or unsymmetrically, are also suitable for the practice of the present invention can be prepared by methods known in the art. E.g., W. Herbst and K. Hunger, Industrial Organic Pigments (New York: VCH Publishers, Inc., 1993), pages 398-415. A particularly preferred isoindoline pigment, Pigment Yellow 139, is a symmetrical adduct of iminoisoindoline and barbituric acid precursors. Dioxazine pigments (that is, triphenedioxazines) are also suitable organic pigments and can be prepared by methods known in the art. E.g., W. Herbst and K. Hunger, Industrial Organic Pigments (New York: VCH Publishers, Inc., 1993), pages 534-537. Carbazole Violet 23 is a particularly preferred dioxazine pigment.
Suitable starting pigments include organic pigments having large particle sizes that do not exhibit good dispersibility or coloristic properties. Such large-particle pigments, even when pretreated with conditioning agents (including acrylic copolymers (1)), do not exhibit significantly improved properties if subsequently collected and only then milled by conventional methods. However, the dispersibility of even pretreated large-particle pigments can be improved by milling in the presence of acrylic copolymers according to the present invention.
Suitable starting pigments also include organic pigments in which the particles, although smaller, are aggregated and thus do not exhibit optimum dispersibility or coloristic properties. For example, many processes that reduce particle size, such as dry milling (e.g., jet milling, ball milling, and the like), can produce aggregates having poor dispersibility and coloristic properties. The process of the present invention can be used to convert such aggregated pigments to readily dispersible forms.
The process of the present invention allows the preparation of pigments having smaller particle sizes than would ordinarily be expected to provide good coloristic or physical properties. It has now been found that pigments prepared by the process of the present invention with very fine particle sizes exhibit excellent coloristic properties and an advantageous combination of dispersibility and rheological properties.
Copolymer Dispersants
Conditioned organic pigments are prepared by the process of the present invention by milling mixtures containing crude organic pigments and acrylic copolymer dispersants. The concentration of the acrylic copolymer dispersant is at least about 0.1 percent by weight (preferably 0.1 to 100 percent by weight, most preferably 2 to 20 percent by weight) relative to the crude organic pigment. Acrylic copolymer dispersants preferably used include at least one adsorbing segment and at least one stabilizing segment. Not to be held to any particular theory, it is thought that adsorbing segments function, in part, to attach a copolymer dispersant to an organic pigment while stabilizing segments function, in part, to maintain dispersion stability of a pigment in a liquid.
An adsorbing segment preferably includes at least one polymerized monomer having an aromatic functionality, more preferably a benzyl functionality. Monomers including an aromatic functionality used to prepare an acrylic polymer dispersant of the present invention are selected, in part, on their theoretical ability to bind to an aromatic pigment. Such a polymerized monomer is prepared from monomers including an aromatic acrylate (such as benzyl acrylate, napthyl acrylate, phenoxy acrylate), aromatic methacrylate (such as benzyl methacrylate, napthyl methacrylate, phenoxy acrylate) or combinations of monomers including an aromatic acrylate. An adsorbing segment may include other polymerized monomers, in addition to polymerized monomers containing an aromatic functionality, and are prepared from monomers such as alkyl (meth)acrylates, alkylaminoalkyl methacrylate monomers having 1 to 4 carbon atoms in the alkyl group (such as dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, dipropylaminoethyl methacrylate, dibutylaminoethyl methacrylate, acrylate esters thereof), or combinations thereof.
A stabilizing segment includes polymerized monomers prepared from monomers such as alkyl(meth)acrylate, methacrylic acid, acrylic acid, silane blocked hydroxy alkyl(meth)acrylate monomers that are subsequently unblocked by a reaction with alcohol or water, or combinations thereof. These hydroxy functionalized monomers may be incorporated to provide sites that allow for crosslinking the copolymer dispersant into the coating system, which in turn enables the dispersant to become part of the network structure and also improves coating adhesion.
Suitable alkyl(meth)acrylates that may be used in the practice of the present invention include those having 1 to 12 carbons in the alkyl group such as methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, pentyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, isopropyl acrylate, butyl acrylate, pentyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, lauryl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, pentyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, lauryl methacrylate and the like and any mixtures thereof.
An acrylic polymer dispersant of the present invention has a number average molecular weight of about 4,000 to about 25,000 (preferably about 5,000 to about 15,000). An adsorbing segment has a number average molecular weight of about 2,000 to about 10,000 (preferably about 4,000 to about 7,000). A stabilizing segment has a number average molecular weight of about 2,000 to about 15,000 (preferably about 4,000 to about 7,000).
The location of an adsorbing segment and a stabilizing segment in an acrylic polymer dispersant may vary depending upon the structure of the acrylic copolymer dispersant. Acrylic polymer dispersants of the present invention may be random, block, or graft copolymers, preferably block copolymers. A block copolymer of the present invention may have an AB, ABA, or ABC structure, for example. At least one of the blocks A, B or C must be an adsorbing segment. At least one of the blocks A, B, or C must be a stabilizing segment. A block copolymer of the present invention may include an additional third segment.
Graft copolymer dispersants of the present invention have a backbone segment and a side chain segment. Either a backbone segment or a side chain segment must be an adsorbing segment. Either a backbone segment or a side chain segment must be a stabilizing segment. Preferably a backbone segment is an adsorbing segment and a sidechain segment is a stabilizing segment.
Random copolymer dispersants of the present invention have both adsorbing segments and stabilizing segments randomly placed in a polymer dispersant chain.
Acrylic copolymer dispersants of the present invention may be prepared using the Group Transfer Polymerization (xe2x80x9cGTPxe2x80x9d) method reported by Webster in J. Amer. Chem. Soc., 105, 5706 (1983); the anionic polymerization method reported by Morton in Anionic Polymerization: Principles and Practice (New York: Academic Press, 1983); the ring-opening polymerization method as reported in Ring Opening Polymerization, Vol. 1, edited by K. J. Ivin and T. Saegusa (New York: Elsevier Applied Science Publishers, 1984), page 461; or the Special Chain Transfer (xe2x80x9cSCTxe2x80x9d) method reported in U.S. Pat. No. 5,231,131.
Milling Liquids
The process of the present invention involves a milling mixture comprising 5 one or more crude organic pigments, one or more acrylic copolymer dispersants, and an optional milling liquid. The quantity of the milling liquid is about 0 to about 100 parts by weight (preferably 1 to 15 parts by weight) relative to the organic pigment.
Suitable milling liquids, if used at all, include water; lower aliphatic alcohols (such as methanol), ketones and ketoalcohols (such as acetone, methyl ethyl ketone, and diacetone alcohol), amides (such as dimethylformamide and dimethylacetamide), ethers (such as tetrahydrofuran and dioxane), alkylene glycols and triols (such as ethylene glycol and glycerol), and other organic liquids known in the art; and mixtures thereof. Other liquids can be used but are generally less preferred.
Milling Additives
Milling additives may also be added in conventional quantities (e.g., 0. 1% to 50% by weight relative to the pigment) to a milling mixture. Examples of suitable milling additives include inorganic compounds (such as metal salts), surfactants, dispersants (such as sulfonamide, carboxamide, or aminoalkyl derivatives of organic pigments, particularly of perylenes, phthalocyanines, or quinacridones), wetting agents, defoamers, grinding aids, latices, or mixtures thereof. In certain cases, one or more inorganic and/or organic bases may be added, especially if the acrylic copolymer dispersant(s) contain acidic functional groups.
Surface Treatment Additives
Before, during, or after milling, a pigment can be treated with a suitable surface treatment additive that may be added directly to the milling mixture. Suitable surface treatment additives include acrylic copolymers; fatty acids (such as stearic acid or behenic acid); corresponding amides, esters, or salts thereof (such as magnesium stearate, zinc stearate, aluminum stearate, or magnesium behenate); resin acids (such as abietic acid, rosin soap, hydrogenated or dimerized rosin); C12-C18-paraffin-disulfonic acids; sulfonated dicarboxylic acids; corresponding esters or amides thereof (such as sulfosuccinates, sulfosuccinamates, and derivatives thereof); lkyl phosphates and phosphonates; long chain fatty amines (such as laurylamine or tearylamine); polyamines (such as polyethylenimines); quaternary ammonium ompounds (such as tri[(C1-C4 alkyl)benzyl]ammonium salts); alkylphenols; alcohols and diols (such as stearyl alcohol and dodecane-1,2-diol); alkoxylated fatty acids and amides, alkoxylated alcohols, alkoxylated alkylphenols, and glycol esters; waxes (such as polyethylene wax); plasticizers (such as epoxidized soya bean oil); or combinations thereof. Such additives can be incorporated in amounts ranging from about 0.1 to 20 percent by weight (preferably 0.1 to 5 percent by weight), based on the amount of the surfactants according to the invention.
Prior to the milling step, the crude organic pigment (or mixture of organic pigments), acrylic copolymer dispersant (or mixture thereof), milling liquid (or mixture thereof), and, if necessary, one or more milling additives and/or one or more surface treatment additives may be combined in any order. Preferably, all such components are combined prior to the milling such that the total solids content in the milling mixture is between 0 and 100 percent by weight (most preferably 15 to 50 percent by weight).
Milling is carried out using known dry milling methods, such as jet milling, ball milling, and the like, or known wet-milling methods, such as salt kneading, sand milling, bead milling, and the like. Although the particular milling apparatus is generally not critical, suitable mills include horizontal mills (for example, Eiger mills, Netzsch mills, and Super mills), vertical mills, ball mills, attritors, vibratory mills, and the like containing various grinding media. Suitable grinding media include salt, sand, glass beads (such as barium titanate, soda lime, or borosilicate beads), ceramic beads (such as zirconia, zirconium silicate, and alumina beads), or metal beads (such as stainless steel, carbon steel, and tungsten carbide beads). Suitable mills and methods are discussed, for example, in U.S. Pat. No. 5,704,556 and Pigment Handbook, Vol. III (New York: John Wiley and Sons, 1973), page 396. Regardless of the particular milling method used, the mixture of the crude organic pigment, the acrylic copolymer dispersant, and the optional components is milled until the desired particle size and particle distribution are obtained. Depending on the specific mill used, milling is generally carried out at a temperature of about 0xc2x0 C. to about 60xc2x0 C. (preferably 15xc2x0 C. to 40xc2x0 C.). Milling times generally depend on the quantities being milled and the volume of the mill. For example, when using a mill having an empty milling chamber volume of 300 to 500 ml, a slurry containing about 300 g of pigment at a solids content of 20 to 25%, is generally milled for about three to about eight hours (typically about five hours).
After the milling step is completed, the pigment or milling mixture can be treated with an optional solvent treatment. Suitable solvents include water; inorganic acids (such as sulfuric or phosphoric acid); organic acids (such as formic or acetic acid); alcohols (such as methanol, ethanol, or ethylene glycol); cyclic or open-chain ethers (such as dioxane, tetrahydrofuran, ethylene glycol monoalkyl or dialkyl ethers, and oligo- and polyglycol ethers); ketones (such as acetone or methyl ethyl ketone); aromatics (such as toluene, xylene, chlorobenzene, nitrobenzene, or chloronaphthalene); esters (such as methyl benzoate, dimethyl phthalate, dimethyl succinate, or methyl salicylate); amides (such as formamide, dimethylformamide, or N-methylpyrrolidone); and mixtures thereof. Solvent treatments are generally carried out at temperatures between about 10xc2x0 C. and about 200xc2x0 C. (preferably at elevated temperatures in the range of 60xc2x0 C. to 145xc2x0 C.).
After the milling, an acid may be added to the milling mixture to promote flocculation (and thereby facilitate isolation), as well as to improve the binding of the acrylic polymer to the pigment surface, particularly for acrylic polymers having acid groups. Suitable such acids include dilute mineral acids (such as hydrochloric, sulfuric, phosphoric, or mixtures thereof); and organic acids (such as acetic, formic or mixtures thereof). Inorganic salts (primarily divalent metal salts), organic salts (primarily quaternary ammonium salts), or mixtures thereof can also be used to flocculate the milled pigment to aid in isolation.
After milling, conditioned pigment maybe separated from the milling mixture by one or more isolation methods known in the art. Filtration, followed by washing to remove residual salts and solvent, is the preferred separation method. Other collection methods known in the art, such as tray drying, spray drying, spin flash drying, lyophilization, centrifugation, or even simple decantation are also suitable isolation methods. Such methods can be used individually or in combination.
Pigments conditioned according to the present invention are suitable for many different pigment applications, particularly in view of their exceptional dispersibility, their light stability, and their migration properties. For example, the conditioned pigments can be dried and used as components in coating systems. Conditioned pigments prepared by the processes of the present invention are readily dispersible, for example, in aqueous coating systems. The conditioned pigments may be mixed with other materials such as pigment formulations (including inorganic white pigments, such as titanium dioxide (rutile), cement, inorganic pigments, flushed pastes with organic liquids or pastes, pigment dispersions with water, dispersants, and, if appropriate, preservatives), coating compositions (including paints, preferably automotive paint, electronic coating paints, physically or oxidatively drying lacquers, stoving enamels, reactive paints, two-component paints, solvent- or water-based paints, emulsion paints for weatherproof coatings and distempers, printing ink, including ink jet inks, or colored paper).
The conditioned pigments of the present invention are suitable for use with macromolecular materials, especially synthetically produced macromolecular materials. Examples include plastic materials, such as polyvinyl chloride, polyvinyl acetate, and polyvinyl propionate; polyolefins, such as polyethylene and polypropylene; high molecular weight polyamides; polymers and copolymers of acrylates, methacrylates, acrylonitrile, acrylamide, butadiene, or styrene; polyurethanes; and polycarbonates. Other suitable macromolecular substances include those of a natural origin, such as rubber; those obtained by chemical modification, such as acetyl cellulose, cellulose butyrate, or viscose; or those produced synthetically, such as polymers, polyaddition products, and polycondensates. Materials containing conditioned pigments of the present invention may have any desired shape or form, including molded articles, films, and fibers.
The following examples further illustrate the present invention and are not intended to limit either the spirit or scope of the present invention. Those skilled in the art will readily understand that other variations exist. Unless otherwise noted, all temperatures are degrees Celsius, all percentages and parts are percentages by weight and parts by weight, respectively.